What to display on a profile page when not logged in

My site has a profile page where users can fill out fields, change their pictures, see stats about themselves, etc.

Currently, if the user somehow lands on profile.html without first being logged in, a sign in modal is opened. If this is closed without logging in, however, they are redirected to our homepage.

This was acceptable until now - we will be sending out a mass email urging users to fill out their profiles. This means that many users will be landing on this page without being logged in, and the redirect will be confusing if and when it occurs.

What is the best practice for showing (but disabling) pages that are behind a login wall? So far I've thought of adding an overlay, disabling interactions with fields, adding a banner prompting to log in, and similar prompts.